Geologists Reconstructed Earth-Moon System 1.25 Billion Years Ago

Analysis of the ancient Hakatai Shale reveals an Earth day lasted 19 hours and provides a new look at lunar distance.

Updated on Sept. 25, 2026 in Geology

A detailed close-up of layered reddish and tan sedimentary rock strata in the Grand Canyon wall. — Researchers identified Milankovic cycles in the 1.25-billion-year-old Hakatai Shale, revealing that Earth's rotation resulted in 19-hour days in the ancient past. AI Illustration. Upload story photo >

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Researchers reconstructed the dynamics of the Earth-Moon system 1.25 billion years ago using sedimentary patterns preserved in the Grand Canyon's Hakatai Shale. This analysis determined that an Earth day lasted approximately 19 hours at the time of the rock's formation.

Why it matters

Understanding ancient celestial mechanics provides critical data on the long-term evolution of the Earth-Moon system and historical planetary rotation rates. These findings fill a gap in geologic history by grounding orbital models in physical sedimentary evidence.

The study measured a 15,730-year precession period by analyzing carbonate-rich and muddy rock cycles in the Hakatai Shale. These patterns indicate the Moon was 53.8 Earth radii away 1.25 billion years ago, differing from other theoretical models of lunar drift.

The players

Nature Geoscience

A monthly scientific journal that publishes high-impact research across all fields of the geosciences.

The details

Researchers examined repeating geological patterns in the Hakatai Shale, a sedimentary formation in the Grand Canyon that originated 1.25 billion years ago on the ancient continent of Laurentia. By comparing alternating rock layers across sites 60 to 65 kilometers apart, the team identified Milankovic cycles—periodic variations in Earth's orbit and rotation that influence climate. These cyclical signatures allowed scientists to calibrate the rotation rate of the ancient Earth.

1.25 billion years ago: The Hakatai Shale layers formed within an inland sea.
September 2026: Researchers published the study results in Nature Geoscience.

The Tech Race

This study updates the long-term timeline of planetary rotation and lunar recession, challenging existing models that predicted different day lengths. It marks a significant effort to reconcile theoretical orbital mechanics with tangible geological evidence from deep-time records.

While these findings concern events from over a billion years ago, they provide the baseline data required to refine modern climate models. This work helps geologists improve the accuracy of chronostratigraphy, the branch of science that determines the relative age of rock strata.

The takeaway

The study demonstrates that Earth's rotation has been gradually slowing over more than a billion years due to lunar tidal interactions. Scientists will now look to apply these sedimentary cycle techniques to other ancient shale formations to further map the history of Earth's rotation.